I don't know the answer to your question about the different yarn types.

However I do not think doing both legs at one time with the really long circular needle(cannot remember it's name) would make a difference with pooling. If I understand correctly you are then working 2 skeins of yarn or using both ends of the same skein of yarn. What comes in handy as I understand it, is after finnishing one leg you don't look at the other and say I STILL have that much to do. Another thing is counting rows. You know when all is said and done both legs will have the same number of rows.

I could be wrong though. I am also a new knitter. I have been knittng for around 8 months now. I have also never done both legs at the same time either.